In a wireless communication system, a network transmits system information to a user equipment, wherein the system information is necessarily required to allow a user equipment to access the network or perform communication with the network. Since all user equipments, which intend to perform communication with the network, require the latest system information, the network broadcasts system information to the user equipments periodically and repeatedly.
The system information can be divided into information blocks such as a master information block (MIB), a scheduling block (SB), and a system information block (SIB). The MIB includes information related to physical configuration of a corresponding cell, such as a bandwidth. The SB includes transmission information of SIBs, for example, information related to transmission period, etc. The SIB is a set of associated system information. For example, some SIB includes only information related to peripheral cells, and another SIB includes only information of uplink radio channels, which a user equipment uses. When the network transmits system information to the user equipment, the network can transmit information blocks one by one or two or more information blocks simultaneously.
To provide multimedia broadcast/multicast service (hereinafter, abbreviated as “MBMS”), control information transmitted from the network to the user equipment is an example of transmitting the same data from the network to the user equipment like system information. For the MBMS, the network provides MBMS control channel (MCCH) and MBMS traffic channel (MTCH). The MCCH is used to transmit control information for MBMS transmission to the user equipment while the MTCH is used to transmit MBMS data to the user equipment. The MBMS is comprised of one or more sessions, wherein only one session can exist during one time interval. In other words, in case of the MBMS, the channel on which user data are actually transmitted is the MTCH, and the channel on which information required to receive the MTCH is the MCCH. MTCH reception establishment information transmitted through the MCCH, i.e., MCCH information is transmitted periodically and repeatedly for the same reason as that of the system information.
The MBMS is to provide a streaming or background service to a plurality of user equipments by using a downlink dedicated MBMS bearer service. In the network, an MBMS bearer uses a point-to-multipoint wireless bearer service or a point-to-point wireless bearer service.
The MBMS is divided into a broadcast mode and a multicast mode. The MBMS broadcast mode is a service for transmitting multimedia data to all user equipments (UEs) within a broadcast area. The broadcast area refers to a region where the broadcast service is possible. On the other hand, the MBMS multicast mode is a service for transmitting the multimedia data to a specific user equipment group only within a multicast area. The multicast area refers to a region where the multicast service is possible.
A procedure of providing a specific MBMS from a network to a user equipment by using a multicast mode will be described below. First of all, user equipments which desire to receive the MBMS should undergo a subscription procedure.
Subscription refers to establishing a relationship between a service provider and a user equipment. Also, the user equipments which desire to receive the MBMS should receive a service announcement provided by the network. The service announcement refers to providing the user equipments with a list of services to be provided and related information of the services.
Meanwhile, a user equipment which desires to receive the MBMS of the multicast mode should join a multicast group specifically. The multicast group refers to a group of user equipments which receive a specific multicast service, and joining refers to merging with a multicast group to receive the specific multicast service. The user equipment can notify the network through the above joining that it desires to receive specific multicast data. On the other hand, the user equipment which has joined the multicast group can unsubscribe to joining of the multicast group, which is referred to as leaving.
Each user equipment performs the subscription, joining and leaving procedures. The user equipment can perform the subscription, joining, and leaving procedures at any time, such as before data transmission, during the data transmission, or after the data transmission.
The MBMS can be divided into a multi-cell service and a single cell service, wherein the multi-cell service is to provide the same service to a plurality of cells, and the single cell service is to provide the same service to a single cell. The multi-cell service is transmitted through a multicast channel (MCH), and the single cell service is transmitted through a downlink shared channel (DL SCH). If the user equipment receives the multi-cell service through the MCH, the user equipment can receive the same multi-cell service transmitted from various cells by combining in an MBMS single frequency network (MBSFN) mode.